Names that fit the chat, and a way to change one

Two things about titles were wrong. Every chat spent a second completion on
its name, including an agent chat whose opening words are already a title --
somebody starting one states an objective, not a topic. An agent chat now
takes `fallback_title` from its first prompt and makes no request at all;
an ordinary chat, which opens with a question whose *answer* is what makes a
title worth asking for, is unchanged.

And renaming existed only as the `/title` slash command, which set the heading
and left the sidebar row showing the old name until the next reload -- a rename
that looks half-applied is one people do twice. There are pencil buttons on the
heading and on every sidebar row now, both PATCHing the route that was already
there, and `update_chat` answers a rename with the out-of-band pair the `done`
frame has always sent, so one response moves both. Only on a rename: sending it
for every PATCH would overwrite the heading from an unrelated save. `/title`
sets both spans itself, being a bare fetch rather than htmx.

The dialog is the `data-prompt` mechanism the folder work added, which is why
the heading keeps a button rather than becoming an inline field: it sits in a
flex row beside the badges and the connection chip, and swapping it for a text
box moves all of them.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/api/chats.py

@@ -1463,12 +1463,14 @@ async def update_chat(request: Request, db: Db, user: RequiredUser, chat_id: str
     allowed = permissions.resolve(db, user)
     form = await request.form()
 
+    renamed = False
     if "title" in form:
         cleaned = str(form["title"]).strip()[:300]
         if cleaned:
             chat.title = cleaned
             # An explicit rename must not be overwritten by auto-titling later.
             chat.title_generated = True
+            renamed = True
 
     if "folder_id" in form:
         chat.folder_id = str(form["folder_id"]) or None
@@ -1576,6 +1578,16 @@ async def update_chat(request: Request, db: Db, user: RequiredUser, chat_id: str
             chat.params_json = {**(chat.params_json or {}), "reasoning_effort": seeded}
 
     db.commit()
+
+    if renamed:
+        # The two out-of-band spans the `done` frame already uses, so one
+        # response updates the heading *and* the sidebar row. Renaming used to
+        # be the `/title` command alone, which set the heading and left the
+        # sidebar showing the old name until the next reload -- a rename that
+        # looks half-applied is one people do twice.
+        return HTMLResponse(
+            templates.get_template("chat/_title_oob.html").render({"chat": chat})
+        )
     return Response(status_code=status.HTTP_204_NO_CONTENT)